1. Field of the Invention
The present invention generally relates to tension control device for a printing paper. More particularly, the present invention relates to an improvement in tension control system for exactly applying tension to an printing paper with ease and accuracy immediately after a initial feeding step is performed in a rotary press.
2. Description of the Prior Art
Since printing paper should be always applied with a stable tension during the printing operation, various tension control and applying devices have been provided. One conventional device is disclosed by Japanese Patent Application Laid-Open Publication No. 55-93756, provided by the same applicant of this invention, entitled "Automatic Tension Control Device for Running Paper at Emergency Stop of Rotary Press". This conventional device is shown in FIG. 5 of the attached drawings of this specification. This drawing corresponds to FIG. 1 in the original publication document. In FIG. 5, a three pronged arms member 1 is pivotably supported on a pivot 2. One end of the three pronged arms member 1 bearing a braking mechanism 3 supports a rolled paper 6 which is rotatably set on a supporting member, not shown, mechanically connected to the braking mechanism 3. Printing paper 7 is drawn from the rolled paper 6 and passed through guide rollers 8 and 8a, a floating roller 9 and a guide roller 8b, and finally introduced into a printing section. The floating roller 9 is pivotably supported on a free end of a swing arm 11, the other end of which is pivotably supported on a pivot 10. The central point of the swing arm 11 is connected to a rod 12a of a pneumatic cylinder 12. The rod 12a supports the swing arm 11, which is subjected to the tension force applied to the printing paper 7, through the floating roller 9. The rod 12a is pressed by pneumatic pressure controlled by a regulator 15, so that the rod 12a can hold the swing arm 11 in a constant position. The pneumatic pressure value Y determined by the regulator 15 corresponds to a tension setting value for the printing paper 7.
When the printing paper 7 is loosened, the swing arm 11 is rotated in the clockwise direction in the drawing. A cam 17 at the pivot side end of the swing arm 11 also rotates and actuates a pressure control valve 16. Predetermined pneumatic pressure is fed from the pressure control valve 16 to the braking mechanism 3 to increase the braking force of the mechanism 3. Thus, the braking mechanism 3 can fixingly hold the rolled paper 6 to prevent the printing paper 7 from drawing.
On the other hand, when the printing paper 7 is stretched with a greater force than a predetermined value, the swing arm 11 is rotated in the counter-clockwise direction in the drawing. According to this motion, the braking force of the braking mechanism 3 is decreased so that the printing paper 7 can be easily drawn from the rolled paper 6.
In such automatic manner the conventional device can always apply a stable tension onto the printing paper 7.
However, the above described conventional device has the following drawbacks in its printing paper feed operation conducted at the first step in printing operation.
The printing paper should be slightly loosened during the paper initial feeding operation because the printing paper cannot be wholly applied with a uniform tension over its width. In the conventional device, the swing arm 11 will rotate in the clockwise direction and increase the braking force of the braking mechanism 3. Therefore, the pneumatic pressure should be released from the braking mechanism 3 in order to draw the printing paper 7 from the rolled paper 6. This requires an additional operation comprising the manual switching of a valve 33 which is switched into an OFF position to release remaining pneumatic pressure from the braking mechanism 3.
After initially feeding the printing paper from the printing section to a paper folding section, another valve 31 is opened and the manual switching valve 33 is switched into an ON position. Successively, the valve 31 is gradually closed and the printing system is driven at a slow speed. This operation gradually increases the braking force of the braking mechanism 3 and starts to run the printing paper 7. Accordingly, the printing paper 7 is gradually applied with tension up to a predetermined value to perform a normal printing work.
The above described series of operations for feeding printing paper 7 and adjusting the tension thereof require the operator to take notice of the condition of the printing paper 7. Further these operations demand complicated and manual operations that need a skilled operator. Therefore, this problem causes various disadvantages such as low working efficiency, high costs, poor product quality, and so on.